Hyakki Yakō

Hyakki Yakō (百鬼夜行; lit. "Night Parade of One Hundred Demons") is a term used for the gathering of yōkai beneath a leader's banner, which can only be mobilized by the leader's command. Though it implies 100 members, such is not always the case - as with Rikuo's Hyakki Yakō, which only contains those with whom he exchanged sakazuki and others willing to follow him. It appears to be an ideal to yōkai, as three of the primary antagonists of the series (Tamazuki, Hagoromo Gitsune and Abe no Seimei) have sought to create a strong Hyakki Yakō. For humans, the term relates to a large group of yōkai traveling at night, often accompanied by rolling fog and unnatural lights or an eerie feel to the air.